Rotary drilling of wells using explosives



time

least 3,083,778 Patented Apr. 2, 1963 3,985,778 ROTARY DRILLENG 9F WELLSUdlNG EXPLGdlVES Robert H. Friedman, Leon H. Robinson, In, and lat-l; H.

Edwards, Houston, Tex assignors, by mesne assignrnents, to JerseyProduction Research Company, Tulsa,

Gide, a corporation of Delaware Filed lviay 25, 1960, Ser. No. 51,365 4Qlaims. (Qt. 175-2) The present invention is directed to the drilling ofwells. More particularly, the invention is concerned with a methed forincreasing the drilling rate in the drilling of oil and gas wells andthe like. In its more specific aspects, the invention is concerned withan improved drilling method in which drilling rates are increased bygeneration of gas adjacent the drill bit.

The present invention may be briefly described as a method for drillinga well with a drill bit in which a hollow drill string, having a drillbit attached to its lower end, is rotated and in which an aqueousdrilling fluid is circulated through a path of flow defined by thehollow drill string and the annulus between the drill string and thewall of the well. The specific feature of the present invention involvesintroducing into the circulating drilling iiuid a suiiicient amount ofwater soluble capsules containing an explosive which is renderedharmless by extended contact with Water. The capsules have a size withinthe range from about 0.01 to about 0.25 inch and the explosive has asensitivity as measured by the dropsensitivity test within the rangefrom about 2 to about 10 cm. The capsules are exploded by weight imposedon the capsules by the drill bit such that increased drilling rates areobtained.

'lhe explosive employed in the practice of the present inventi n shouldbe an explosive which is moderately sensitive in the range from about 2to about 10 cm. as measured by the standard drop-sensitivity test. Thistest measures the height in centimeters; a 2 kilogram weight must bedropped to cause explosion. A description of this test will be found inMeyer, Martin, Explosives, Thomas Y. Crowell Co., New York, 1943, p. 28.The preferred range of sensitivity is in the range from about 2 to about5 centimeters.

While the exact composition of the explosive is not critical, theexplosive must have the sensitivity set out hereiubefore. As examples ofthe explosives which are useful in the present invention, there may bementioned lead picrate and guhr dynamite. These explosives are withinthe preferred range of sensitivity. Explosives that are in themselvesabove the range of sensitivity may be brought to the desired sensitivityby admixture with more sensitive materials which function as igniters.Admixture serves to decrease the sensitivity of the more sensitivematerial and increase that of the less sensitive material. Thus, byadmixing such explosives as mercury fulminate, for example 80 percentmercury fulminate with 20 percent potassium perchlorate; or antimonytrisulfide, lead triazide, or nitrogen triiodide with standardexplosives like dynamite, trinitrotoluene, and PETN (pentaerythritoltetranitrate), the sensitivity may be adjusted to a sensitivity withinthe desired range. A desirable characteristic of the explosive is thatit is rendered harmless by contact with water. Contact with waterprevents dangerous accumulation of the explosives in the drilling fluid.

The encapsulating agent for the explosive may be any water impervious,slow-dissolving material. Typical of such materials are the naturalgums, such as gelatine, gum araoic, gum tragacanth, or guar seed gum.Other satisfactory materials are the synthetic materials commonly usedto encapsulate medicines, polyvinyl alcohols, carboxylated methylcelluloses, or organic compounds slowly soluble in water such asbenzoin, camphor or diphenylurea. The granulated, encapsulated explosiveshould have a particle size in the range from about 0.01 to about 0.25inch and preferably in the range from about 0.05 to about 0.15 inch.

The amount of the explosive capsules added to the drilling fluid is inthe range from about 0.1 to about 10 lbs. per barrel of drilling fluid.A preferred concentration is from about 1 to about 5 lbs. per barrel ofdrilling fluid. The explosive capsules are preferably added to thedrilling mud intermittently but may be added continuously so long as thedesired concentration is maintained in the drilling mud and there issufiicient explosive concentrated in the region of the drill bit or inthe filter cake on the bottom of the well.

Inasmuch as it is necessary for the capsules to dissolve slowly in waterto prevent dangerous accumulation thereof, it is necessary to use anaqueous drilling fluid. In other words, the drilling fluid must containwater to contact the encapsulated explosive such that in case any of thecapsules are not exploded by setting down weight thereon by the drillbit, the explosive will be rendered harmless by dissolution of thecapsules and contact of the explosive with water.

It will be desirable to provide materials as encapsulating agents whichwill dissolve in a period of time such that the encapsulating materialwill slowly dissolve. Thus, the capsules will dissolve at a time withinthe range from 10 minutes to 10 days such that the explosive is renderedharmless. Little, if any, of the explosive will be in the mud returnedto the earths surface in that most, if not all, of that which is notexploded will be dispersed in the filter cake lining the wall of thewell bore. Additionally, the concentration of 0.1 to 10 lbs. of smallgrain encapsulated explosive in such that it will be Widely dispersed inthe drilling fluid.

The present invention will be further illustrated by reference to thedrawing in which:

FIG. 1 is allow diagram of a preferred mode; and

PEG. 2 illustrates a mode for encapsulating the explosive.

Referring now to the drawing, numeral 11 designates the earths surfacefrom which a well bore 12 has been drilled by rotating a hollow drillstring 13 carrying on its lower end a rock bit 14, suitably a toothedbit, but other well-known rock bits may be used. The hollow drill stringextends to the floor 15 of a derrick 16 wherein it is rotated by arotary table 17 driven by a suitable power means, not shown. (Ionnectedinto the upper end of the drill string 13 is a kelly joint 13 whichconnects by means of a swivel 19 to a flexible conduit 20 which, inturn, connects by pipe 21 to a mud pump 22. Mud pump 22 takes suction bypipe 23 with the mud pit 24.

Connected into pipe 21 by a conduit 27 controlled by a valve 28 is atank 29 which contains a supply of encapsulated explosives. As the mudis drawn into the pump 22 through line 23 and pumped by line 21 asufficient amount of the encapsulated explosive is discharged by line 27into line 21 to maintain in the drilling mud the desired concentrationof explosive and the mud con taining the explosive is then pumped downthe hollow drill string 13 and out through the drill bit 14. Theexplosive then concentrates in the filter cake at the bottom of the wellbore and the concentrated encapsulated explosive is then crushed by theweight of the drill string and thus exploded. By virtue of the explosionof the explosive by the drill bit 14, the drilling rate is enhanced to aconsiderable degree by microscopic fissures or cracks created under thedrill bit by the plurality of explosions occurring. v"Ihis allows thedrill bit to fracture the rock formation easily and results in increaseddrilling rates. Not only is the present invention useful in increaseddrilling rate but explosions in the region of drill bit 14 causemicroscopic fissures in the rock which allows the rock to be fracturedeasily by the drill bit and removed as chips. With generation of gas inthe immediate vicinity of the rock bit teeth, the pressure differentialacross the rock chips is reduced and the rock chips are efficientlydislodged and microscopic fissures that are formed are widened ratherthan healed as encountered in conventional drilling operations.

The exploding capsules 30- thus create a plurality of miniatureexplosions 31 in the region of the rock bit 14 speeding the drillingrate and allowing improved drilling operations.

Any of the capsules which emerge from under the drill bit 14 withoutexploding are carried into the annulus 32 and deposited in the filterca'ke lining the well bore wall and by virtue of the time elapsing, thecapsules are slowly dissolved and the explosives are eventually renderedharmless by contact with the aqueous drilling fluid.

The present invention is quite advantageous and useful in increasing thespeed of drilling through earth formations.

Referring now to FIG. 2, a mode is described of encapsulating thegranulated explosive. In FIG. 2, numeral 40 designates a hoppercontaining granulated explosive 41 of sufiiciently small size to formcapsules of a size within the range given. The hopper 40 is controlledby valve 42 which allows a stream 43 of the granulated explosive 41 tobe discharged into a tank 44 containing a volume 45 of encapsulatingagent such as has been described. The stream 43 of the granulatedexplosive 41 falls downwardly within the encapsulating agent 45 and iscoated thereby and by gravity flows into the boot 46 for removal of theencapsulating agent by way of line 47 controlled by valve 48. Theencapsulated explosive may then be dried as desired and then placed inthe tank 29 for introduction into line 21 as has been described. Whileone method has been described of encapsulating the granulated explosive,other methods may be used. For example, the explosive may beencapsulated by a spray-drying technique.

The practice of the present invention has been illustrated byconventional circulation down the drill string and up the annulus. It isto be understood, however, that reverse circulation may be employed suchthat the mud is flowed down the annulus 32 and up the drill string 13.In such instances, of course, it would be necessary to change the flowsystem to provide for returns of the mud to the mud pit.

The nature and objects of the present invention having been completelydescribed and illustrated, what we wish to claim as new and useful andsecure by Letters Patent is:

1. In the drilling of a well by rotating a hollow drill string having adrill bit attached to its lower end and in which an aqueous drillingfluid is circulated through a path of flow defined by the hollow drillstring and the annulus between the drill string and the wall of the wellwherein the well is drilled with said bit, the step of introducing intothe circulating drilling fluid a sufiicent amount within the range fromabout 0.1 to

pounds per barrel of drilling fluid of water soluble capsules containingan explosive which would eventually be rendered harmless by extendedcontact with Water, said capsules having a size within the range fromabout 0.01 to about 0.25 inch, said explosive having a sensitivity asmeasured by the drop-sensitivity test within the range from about 2 toabout 10 cm., said capsules being circulated to and discharged under thedrill bit and there exploded by weight imposed on said capsules by saiddrill bit whereby increased drilling rates are obtained.

2. A method in accordance with claim 1 in which the amount of capsulesis within the range from about 1 to about 5 pounds per barrel ofdrilling iluid and in which the size is within the range from about 0.05to about 0.15 inch.

3. In the drilling of a well by rotating a hollow drill string having adrill bit attached to its lower end and in which an aqueous drillingfluid is circulated through a path of flow defined by the hollow drillstring and the annulus between the drill string and the Wall of the wellwherein the well is drilled with said bit, the steps of introducing intothe circulating drilling fluid a suflicient amount within the range fromabout 0.1 to about 10 pounds per barrel of drilling fluid of watersoluble capsules of an explosive which would eventually be renderedharmless by contact with water for a time within the range from about 10minutes to about 1 0 days, said capsules having a size within the rangefrom about 0.01 to about 0.25 inch, said explosive having a sensitivityas measured by thedrop-sensitivity test within the range from about 2 toabout 10 cm., said capsules being circulated to and discharged under thedrill bit and there exploded by weight imposed on said capsules by saiddrill bit whereby increased drilling rates are obtained.

4. In the drilling of a well with a drill bit in which an aqueousdrilling fluid is circulated in the well wherein the well is drilledwithsaid bit, the steps of introducing into the circulating drillingfluid a sui-ficient amount within the range from about 0.1 to about 10pounds per barrel of drilling fluid of water soluble capsules containingan explosive which would eventually be rendered harmless by contact withwater, said capsules having a size within the range from about 0.0'1 toabout 0.25 inch, said explosive having a sensitivity as measured by thedropsensitivity test within the range from about 2 to about 10 cm., saidcapsules being circulated to and discharged under said drill bit andexploded by weight imposed on said capsules by said drill bit, wherebyincreased drilling rates are obtained.

References Cited in the file of this patent UNITED STATES PATENTS476,757 Miller June 7, 1892 1,582,256 Franklin Apr. 27, 1926 2,155,499Lawson Apr. 25, 1939 2,209,591 Barnes July 3 0, 1940 2,337,296 KennedyDec. 21, 1943 2,544,573 Vincent Mar. 6, 1951 2,745,346 Aitchison et al.May 15, 1956. 2,897,756 Borins et al. Aug. 4, 1959 OTHER REFERENCESNeeded Now: a Better Understanding of the Basics of Earth Boring, L. W.Ledgerwood, Jr., Oil and Gas Journal, volume 58, No. 19, May 9, 1960.

1. IN THE DRILLING OF A WELL BY ROTATING A HOLLOW DRILL STRING HAVING ADRILL BIT ATTACHED TO ITS LOWER END AND IN WHICH AN AQUEOUS DRILLINGFLUID IS CIRCULATED THROUGH A PATH OF FLOW DEFINED BY THE HOLLOW DRILLSTRING AND THE ANNULUS BETWEEN THE DRILL STRING AND THE WALL OF THE WELLWHEREIN THE WELL IS DRILLED WITH SAID BIT, THE STEP OF INTRODUCING INTOTHE CIRCULATING DRILLING FLUID A SUFFICENT AMOUNT WITHIN THE RANGE FROMABOUT 0.1 TO 10 POUNDS PER BARREL OF DRILLING FLUID OF WATER SOLUBLECAPSULES CONTAINING AN EXPLOSIVE WHICH WOULD EVENTUALLY BE RENDEREDHARMLESS BY EXTENDED CONTACT WITH WATER, SAID CAPSULES HAVING A SIZEWITHIN THE RANGE FROM ABOUT 0.01 TO ABOUT 0.25 INCH, SAID EXPLOSIVEHAVING A SENSITIVITY AS MEASURED BY THE DROP-SENSITIVITY TEST WITHIN THERANGE FROM ABOUT 2 TO ABOUT 10CM., SAID CAPSULES BEING CIRCULATED TO ANDDISCHARGED UNDER THE DRILL BIT AND THERE EXPLODED BY WEIGHT IMPOSED ONSAID CAPSULES BY SAID DRILL BIT WHEREBY INCREASED DRILLING RATES AREOBTAINED.